stoichometry

Question 1

what is relative atomic mass (Ar)

Answer 1

the average mass of naturally occuring atoms of an element on a scale where the 12C atom has a mass of exactly 12 units

Question 2

formula for Ar

Answer 2

((% of isotope a x mass of isotope a) + (% of isotope b x mass of isotope b))/100

Question 3

avogadros constant

Answer 3

6.02 x 10^23

Question 4

triangle for finding moles of all substances

Answer 4

mass/moles x relative formula mass

Question 5

triangle for finding moles of gases

Answer 5

volume of gas (dm^3) / number of moles of gas x 24

Question 6

triangle for finding moles of solutions

Answer 6

amount in moles (mol)/ concentration (mol/dm3) x volume (dm^3)

Question 7

steps for calculating empirical formula

Answer 7

Step
1 Write the element symbols C H
2 Write the masses 4.8 g 1.0 g
3 Write the Ar values 12 1
4 Divide masses by Ar 4.8 ÷ 12 = 0.4 1.0 ÷ 1 = 1
5 Divide by the smallest number 0.4 ÷ 0.4 = 1 1.0 ÷ 0.4 = 2.5
6 Multiply (if needed) to get whole numbers 1 × 2 = 2 2.5 × 2 = 5
7 Write the formula C2H5 C2H5

Question 8

formula for percentage yield

Answer 8

(experimental yield/theoretical yield) x 100

Question 9

formula for percentage purity

Answer 9

(amount of pure substance/amount of impure substance) x 100